Anode assembly for lithium-halogen cell

ABSTRACT

An anode assembly for a lithium-halogen cell including halogen-containing cathode material, i.e. depolarizer, such as an iodine-organic complex wherein the anode comprises an electrical conductor sandwiched between a pair of lithium plates defining substantially oppositely directed lithium surfaces terminating in a peripheral lithium edge and characterized by a major portion of the length of the peripheral edge being exposed to the cathode material. This greatly increases the available internal volume of the cell for cathode material which, in turn, increases the theoretical ampere-hour rating of the cell. At least one and preferably both oppositely directed lithium surfaces have formations such as ribs or the equivalent which increases the surface area thereof, and the formations terminate a short distance from the edge to form a marginal type, peripheral border and highly effective seal therearound. The inner surfaces of the lithium plates can include co-operating formations near the peripheral edge shaped to expose new surfaces of the lithium plates to each other to form or enhance the bond therebetween. The anode assembly is formed using mold sections of a polyolefin material such as a high density polyethylene or equivalent material and having tapered recesses to provide effective separation of the anode from the mold without any need for parting sheets.

This is a continuation of application Ser. No. 222,498 filed Jan. 5,1981.

BACKGROUND OF THE INVENTION

This invention relates to the conversion of chemical energy toelectrical energy, and more particularly to a new and improved anodeconstruction for lithium-halogen cells and method of making the same.

One area of use of the present invention is in providing electricalpower to inaccessible devices in the human environment, for example toan implanted cardiac pacemaker, although the principles of the presentinvention can be variously applied. Lithium-iodine batteries areavailable for such use and advantageously have an open circuit voltageof about twice that of the mercury cell, do not generate gas duringoperation, and have a non-corrosive electrolyte.

It is desirable to maximize that portion of the internal cell volume forcontaining cathode material which in turn increases the theoreticalampere-hour rating of the cell. It is also desirable to maximize thelithium anode surface area in direct operative contact with the cathodematerial. In addition, the nature of the iodine-containing cathodematerial such as an iodine complex is that it can tend to flow withinthe cell and possibly form a short circuit path between the anodecollector lead and the cathode. Therefore it is important to preventsuch leakage.

SUMMARY OF THE INVENTION

It is, therefore, an object of this invention to provide a new andimproved anode for a lithium-halogen cell.

It is a further object of this invention to provide such an anode havingan increased surface area for operative contact with the cathodematerial, i.e. depolarizer, in the cell.

It is a further object of this invention to provide such an anode havinga structure which increases the portion of the internal cell volume forcontaining depolarizer material and thereby increasing the theoreticalampere-hour rating of the cell or, alternatively, permitting the entireouter dimensions of the cell to be reduced while maintaining the sametheoretical ampere-hour rating.

It is a further object of this invention to provide such an anode withan enhanced seal of the anode conductor therein providing improvedisolation from the iodine-containing cathode material in the cellcasing.

It is a further object of this invention to provide a method of makingsuch an anode of the type including an anode current collectorsandwiched between a pair of lithium plates characterized by providingimproved lithium-lithium cohesion.

It is a more particular object of this invention to provide such amethod which accomplishes improved lithium-lithium cohesion using lowerpressing forces.

It is a further object of this invention to provide such an anode thatenables the cell to have fewer parts, to be easier to manufacture, andto be more reliable in operation.

It is a further object of this invention to provide such an anodeassembly wherein the lithium area therein is relatively large and theoverall size is relatively small.

It is a further object of this invention to provide a new and improvedapparatus for making an anode for a lithium halogen cell including amold which readily separates from the lithium anode after forming.

The present invention provides an anode assembly and method of makingsame for a lithium halogen cell including halogen-containing cathodematerial, the anode assembly comprising an anode electrical conductorsandwiched between a pair of lithium plates defining substantiallyoppositely-directed lithium surfaces terminating in a peripheral lithiumedge and characterized by a major portion of the length of theperipheral edge being uncovered and exposed. Additionally, areas of theoppositely-directed lithium surfaces adjacent to the major portion ofthe peripheral edge also are uncovered and exposed. At least one andpreferably both of the oppositely-directed lithium surfaces are shapedto include formations which increase the surface area thereof, and theformations terminate a short distance inwardly of the peripheral edgethereby defining a marginal border region between the peripheral edgeand the formations. The inner mating surfaces of the lithium platesunder the marginal border region experience increased pressing movementduring formation of the anode with lower pressing force resulting in agreatly increased lithium-lithium bond therebetween. Alternatively, theinner surfaces of the lithium plates can be formed to includeco-operating formations that are shaped to expose new surfaces of thelithium plates to each other which in mating enhance the bondtherebetween. The anode assembly is formed by an apparatus including apair of mold type sections or plugs of polyolefin material, such aspolyethylene, having sufficient density and provided with surfaceformations shaped to provide a mechanical release thereby providingeffective separation of the lithium anode from the plugs after theforming operation. The apparatus further includes a segmented nest orring type device for imparting shape to the formed anode, and portionsof the nest which contact the lithium anode also are of polyolefinmaterial, for example high density polyethylene, or the equivalent.During use the apparatus surrounds the assembly at the periphery of thelithium elements and allows release of the lithium anode after theforming operation without requiring the use of parting sheets.

The foregoing and additional advantages and characterizing features ofthe present invention will become clearly apparent upon a reading of theensuing detailed description together with the included drawing wherein:

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 is a perspective view of a lithium-iodine cell including an anodeassembly according to the present invention;

FIG. 2 is a sectional view taken about on line 2--2 in FIG. 1;

FIG. 3 is a sectional view taken about on line 3--3 in FIG. 1;

FIG. 4 is a sectional view taken about on line 4--4 in FIG. 3;

FIG. 5 is a fragmentary elevational view illustrating one stage of amethod of forming the anode assembly according to the present invention;

FIG. 6 is a fragmentary elevational view illustrating another stage ofthe method of FIG. 5;

FIG. 7 is a fragmentary elevational view illustrating one stage of amethod according to an alternative embodiment of the present inventionshown prior to pressing;

FIG. 8 is a fragmentary elevational view illustrating another stage ofthe method of FIG. 7 shown after pressing;

FIG. 9 is an elevational view of a portion of the apparatus forfabricating the anode assembly according to the present invention;

FIG. 10 is an enlarged fragmentary sectional view taken about on line10--10 in FIG. 9; and

FIG. 11 is an elevational view of another portion of the apparatus forfabricating the anode assembly according to the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring now to FIG. 1, a lithium-iodine cell having an anode accordingto the present invention comprises a casing 10 of metal such asstainless steel which preferably is shaped or otherwise formed to behollow and generally rectangular in shape of an integral constructionincluding a bottom portion 11, spaced-apart planar side wall portions12,13 extending from the bottom portion, and spaced-apart curved endwall portions 14,15 also extending from bottom portion 11 and joiningcorresponding ones of the side wall portions 12, 13. The bottom portion11 is of compound shape in that it is curved in a direction between theside wall portions 12, 13 and has a straight section between the endwall portions 14, 15. The curvature of bottom portion 11 between sideportions 12, 13 is of the same degree as the curvature of the end wallportions 14, 15 thereby defining a continuous, curved surface around thecasing. The side wall portions 12, 13 are generally parallel. Casing 10has an opened top or end opposite the bottom portion 11 which is sealedclosed by means of a lid 17 also of metal such as stainless steel afterthe cell has been assembled as will be described in detail presently.

Referring now to FIGS. 2 and 3, the anode of the present inventioncomprises a pair of lithium elements or plates 22,24 having an anodeelectrical conductor 26 sandwiched or positioned therebetween. In theanode assembly shown, conductor 26 is one portion or length extendingfrom another portion or length 30 of the anode conductor which portion30 extends from portion 26 at about a right angle and is of sufficientlength allowing it to extend out from casing 10 for making electricalconnection thereto. The anode electrical conductor comprising portions26,30 is of nickel, nickel-iron alloy or other suitable metal. Variousalternative arrangements can be employed, such as portion 26 being inthe form of one or more strands or ribbons, or having a larger screenattached thereto, or a plurality thereof and such as portions 26 and 30having a common longitudinal axis substantially perpendicular to theplane of lid 17 so that a straight anode conductor is provided. In thecell shown the conductor portion 26 is relatively narrow in width andcontacts only minor portions of the surface areas of the inner surfacesof the lithium plates 22,24. The narrow conductor portion 26 functionswell and may not be large in area unless so desired since lithium is aconductive metal.

The portion or length 30 of the anode conductor is sealed from theremainder of the cell by means including an insulator element generallydesignated 32 which surrounds conductor portion 30 and which insulatorhas a first body portion 34 which is sandwiched between the plates 22,24and a second body portion 36 which is of larger cross section,preferably cylindrical, and located between the lithium plates and lid17 when the cell is completed. The longitudinal axis of insulator 32 isgenerally coincident with the longitudinal axis of lead portion 30. Theinsulator 32 is of a material which in addition to being a non-conductorof electricity also is non-reactive with iodine, i.e. does not exhibitelectronic conduction when exposed to halogens such as iodine. One formof material found to perform satisfactorily is a fluoropolymer materialcommercially available under the name Halar, a trademark of the AlliedChemical Company. Other materials such as Tefzel, a trademark of theDupont Company, or others having these characteristics can of course beused for the insulator 32.

The anode conductor sealing means further comprises an isolator elementgenerally designated 42 located between insulator 32 and conductor 30.In particular, isolator 42 includes a first portion 44 having an outerdimension enabling it to fit relatively snugly within insulator portion34 and a second portion of a size and shape enabling it to be receivedwithin insulator portion 36. Isolator 42 has a longitudinal passage orbore along the entire length of isolator 42 and of a cross-sectionaldimension enabling it to receive anode conductor portion 30. Theisolator element 42 is of a material which does not exhibit electronicconduction when exposed to halogens such as iodine. One form of materialfound to perform satisfactorily is the previously mentionedfluoropolymer material commercially available under the name Tefzel.

The anode conductor sealing means further comprises a ferrule 52 ofmetal such as stainless steel which encloses a further portion of lead30. Ferrule 52 is of generally hollow cylindrical shape withsubstantially constant outer diameter proceeding from one end 53 towardcasing 10 as viewed in FIG. 2, and ferrule 52 has a slightly largerouter diameter which increases stepwise in the region adjacent lid 17.The end of ferrule 52 opposite end 53 has portions which contact endportions of insulator 32 and isolator 42. The longitudinal axis offerrule 52 is generally coincident with the longitudinal axis ofconductor 30. The inner diameter of ferrule 52 is substantially constantproceeding from the one end and continuing along with the largerdiameter portion. The anode conductor portion 30 extends through ferrule52 along the longitudinal axis thereof and spaced substantiallyequidistant from the inner surface of ferrule 52. A cylindrical sealelement (not shown) of glass having an axial bore to receive conductorportion 30 is fitted within ferrule 52. The seal element preferablyextends from the ferrule end face 53 along a major portion of the lengthof ferrule and has an inner end portion which may contact an end portionof isolator 42.

The internal structure and arrangement of insulator 32, isolator 42 andferrule 52 can be as shown and described in U.S. Pat. No. 4,166,158issued Aug. 28, 1979 or in U.S. Pat. No. 4,210,708 issued July 1, 1980both assigned to the assignee of this invention, and the disclosures ofboth patents are hereby incorporated by reference.

As shown in FIGS. 2 and 3, the anode assembly of the present inventioncomprises the anode electrical conductor 26,30 sandwiched between thepair of lithium plates 22,24 defining substantially oppositely-direcedlithium outer surfaces which terminate in a marginal or peripheral edge60. The anode assembly of the present invention is characterized by amajor portion of the length of the peripheral edge 60 being uncoveredand exposed to cathode material in the cell. In the anode assemblyshown, for example in FIG. 3, the uncovered and exposed portion of thelength of the peripheral edge 60 includes the relatively straight bottomportion which faces the casing bottom 11, upwardly curved portions ateach end of the bottom portion, and an inclined or angled portion at thelefthand end as viewed in FIG. 3. The areas of the oppositely-directedlithium surfaces adjacent to the aforementioned major portion ofperipheral edge 60 also are uncovered and exposed to cathode material inthe cell. In the anode assembly of the present invention a minor portionof the length of the peripheral edge can be covered by an element 64 ofelectrically insulating material if so required. Element 64 is in theform of a band or strap which is relatively thin and may have a widthlarger than the width of the anode. In the anode assembly shown, forexample in FIG. 3, element 64 extends along a flap top portion of thelength of the peripheral edge which faces lid 17 and is generallyparallel to the lid and further extends along a right angle step portionagainst which insulator portion 36 rests. In the cell shown, the sectionof element 64 along the flap top portion of the anode peripheral edgecontacts the inner surface of lid 17 but alternatively could be spaced ashort distance therefrom. In addition, the insulating element 64 may beeliminated if the anode lithium elements 22,24 are spaced from lid 17 adistance sufficient to avoid any electrical short circuit conditions. Asa result, cathode material in the cell not only contacts the oppositelydirected surface portions of the lithium elements 22,24 but alsocontacts a major portion of the peripheral edge 60 as well as areas ofthe oppositely directed surfaces immediately adjacent the major portionof the peripheral edge. As a result the anode has an increased surfacearea which operatively contacts cathode material or depolarizer in thecell. The foregoing anode structure, characterized by a major portion ofthe length of peripheral edge 60 and the adjacent areas of theoppositely directed surfaces being uncovered and exposed, results in anincreased cell internal volume for containing depolarizer material.This, in turn, increases the theoretical ampere-hour rating of the cell.Alternatively, the foregoing anode structure permits the outer size ofthe cell to be reduced while maintaining the same theoreticalampere-hour rating of the cell.

In the anode assembly according to the present invention at least oneand preferably both of the oppositely-directed lithium surfaces ofplates 22,24 is shaped to include formations which increase the surfacearea thereof. Referring to FIG. 3 the formations are designated 70 andeach formation is elongated having terminations at both ends thereof.The terminations are spaced inwardly a short distance from theperipheral edge of the anode assembly thereby defining a marginal borderregion between the peripheral edge and the termination of theformations. The formations 70 are generally mutually parallel, and arealso generally parallel to the common longitudinal axes of ferrule 52and the section of lead 30 therein. The formations 70, which are in theshape of ribs or corrugations, have generally smooth outer surfaces andpreferably are generally semi-circular in cross-section. In the anodestructure shown, the sections between adjacent ribs 70 haveoppositely-directed smooth surfaces. The ribs occupy a major portion ofthe outer surface area of each lithium element 22,24. The remainingsurface portions are generally planar and mutually generally parallelexcept around insulator portion 34 and isolator portion 44 where theyare curved or outwardly bulged.

One illustrative method of forming the anode assembly is as follows.First there is provided an subassembly including the combination ofinsulator 32, isolator 42, ferrule 52 and conductor portions 26,30 withconductor portion 30 being within the combination of insulator 32,isolator 42, and ferrule 52. Briefly, isolator 42 is assembled intoferrule 52, and then the combination of isolator 42 and ferrule 52 isjoined to insulator 32. For a more detailed description of theforegoing, reference may be made to the afore-mentioned U.S. Pat. Nos.4,166,158 or 4,210,708. The insulator strip 64 then is assembled intoplace, the strip having an opening therein enabling it to be fitted ontoinsulator portion 34 as shown in FIG. 3. It can be joined to insulatorparts 34,36 by means of a suitable cement which is non-reactive withiodine such as a cyanoacrylate cement commercially available from thePearl Chemical Co. under the name Permabond 101. During an earlier stageof the method, the end of isolator portion 44 and section of conductor26 contained therein were bent or otherwise curved as a unit by asuitable tool to the left as viewed in FIG. 3 to form substantially aright angle with the portion 30 and longitudinal axis of ferrule 52. Thelithium plates 22,24 then are positioned on opposite sides of theconductor 26 and insulator portion 34. As shown in FIG. 3, the step orrectangular shoulder on the peripheral edge of the lithium platecombination abuts against the lower surface of insulator portion 36, theinsulator strip being therebetween. Strip 64 extends along the topportion as viewed in FIG. 3 including the right angle step adjacent toinsulator portion 36. The subassembly then is placed within two moldsections and is pressed together with a suitable force, for exampleabout 2,000 pounds. The conductor 26, insulator portion 34 and thesection of lead 30 contained therein are sealed within the lithiumelements 22,24. The inner surfaces of the two mold sections are shapedto define the rippled or corrugated outer anode surface formations shownin FIGS. 3 and 4. Removal of the anode from the mold can be facilitatedby employing two parting sheets, preferably of polyethylene, one betweeneach of the mold sections and the corresponding outer surfaces of theanode. However, according to another aspect of this invention which willbe described in detail presently, no parting sheets are necessarybecause the molds and a portion of the anode pressing apparatus are madeof a polyolefin material, such as high-density polyethylene orequivalent material, which has been found not to adhere readily to thelithium but rather to allow the lithium to be removed from the molds andthe pressing apparatus after the pressing operation and without the useof parting sheets.

As shown in FIG. 4, the oppositely directed lithium anode surfaces areformed to have the spaced, generally mutually parallel ribs orcorrugations 70 which extend parallel to the common longitudinal axes offerrule 52 and the section of lead 30 therein. The formations or ribs 70have generally smooth outer surfaces which preferably are generallysemi-circular in cross-section. In the anode structure shown, thesections between adjacent ribs have oppositely directed smooth surfaces,and the common thickness of the sections is about one-half the overallthickness measured from the outer tip of one corrugation to the outertip of the aligned corrugation on the opposite face of the anodestructure, although this can vary. The ribs 70 occupy a major portion ofthe surface area of each lithium element 22,24. The remaining surfaceportions ae generally planar and mutually generally parallel exceptaround insulator portion 34 and isolator portion 44 where they arecurved or outwardly bulged, and may completely pocket the insulator 34and the isolator 44. This formation to enclose the insulator andisolator portions also is defined by the mold sections. The material ofstrip 64 may be bonded to the lithium elements 22,24 by applying theaforementioned Permabond or equivalent cement to strip 64 after theanode pressing operation to enhance its adhesion. The strip 64 maylikewise be bonded to the lithium elements 22,24 if so desired beforethe anode is pressed. The finished anode assembly thus has two exposedsurfaces which are oppositely directed.

FIGS. 5 and 6 illustrate in further detail the method of forming theanode assembly according to the present invention. A subassembly isprovided in the manner described hereinabove and is placed along withthe lithium plates 22,24 within two mold sections as previouslydescribed. Fragmentary peripheral portions of the two mold sections aredesignated 74 and 76 in FIGS. 5 and 6 which also show fragmentaryperipheral portions of the lithium plates 22,24 of the subassemblybetween the mold sections. The inner surfaces of mold sections 74 and 76are provided with spaced recesses 80 and 84, respectively, for providingthe anode ribs. FIG. 5 shows the arrangement before pressing and FIG. 6shows the arrangement after the mold sections 74,76 have been broughttogether and pressed against the subassembly and after the applicationof suitable force, for example about 2000 pounds. The lithium plates22,24 are bonded together, and the recesses 80,84 in the mold sectionsdefine the ribs or corrugations 70 in both opposite faces of the anodeassembly.

The foregoing method results in greatly improved lithium-to-lithiumcohesion in the resuting anode assembly after pressing. This is believedto be created by an unimpeded and uninterrupted flow or movement of thelithium upon itself or between both lithium plate surfaces and by thecontinuous marginal or peripheral border 88 of the anode assemblyaccording to the present invention. In other words, there is nomarginal, peripheral strap or frame around the greatest portion of theanode assembly of the present invention to restrict such flow. Thestrap, or in this case element 64, i.e. the separator, can be completelyeliminated by spacing the lithium plates 22 and 24 a sufficient distancebelow the lid 17 so that no electrical shorting will ensue. The ribs 70terminate inwardly of the periphery of the lithium plates to define theborder 88 completely around the anode and on both opposite facesthereof. In addition, in the method of the present invention,significantly less pressure is required to form and bond the lithium andyet the lithium cohesion is markedly increased.

FIGS. 7 and 8 illustrate an alternative method of forming an anodeassembly according to the present invention. A subassembly is providedin the same manner as in the foregoing method and is placed along withthe lithium plates l22',24' within two mold sections. Fragmentaryperipheral portions of the two mold sections are designated 74',76' inFIGS. 7 and 8 which also show fragmentary peripheral portions of thelithium plates 22',24' positioned between the mold sections. The uppermold section 74' as viewed in FIGS. 7 and 8 is provided with aprotuberance or extension 78 on the inner or working face of the moldadjacent the peripheral edge. Protuberance 78 preferaly is continuous,extending around the entire periphery of mold section 74' and in thearrangement illustrated in FIGS. 7 and 8 has a substantiallysemi-circular or curved outer surface so as to be bead-like.Alternatively, protuberance 78 could be of rectangular shape for ease inmachining. Spaced within protuberances 78 the inner surface of moldsection 74' is formed with spaced recesses, two of which are designated80', for providing the anode ribs 70'. The lower mold section 76' asviewed in FIGS. 7 and 8 is provided with a recess 82 on the inner orworking face of the mold adjacent the peripheral edge. Recess 82preferably is continuous, extending around the entire periphery of moldsection 76' and in the arrangement illustrated in FIGS. 7 and 8 has asubstantially semi-circular or curved inner surface so as to mate withprotuberance 78. Alternatively, recess 82 could be of rectangular shapefor ease in machining. In addition, recess 82 is located on the face ofmold section 76' so as to be in registry with protuberance 78 when themold sections 74',76' are brought together. Spaced within recess 82 theinner surface of mold section 76' is formed with spaced recesses, two ofwhich are designated 84', for providing anode ribs 70'.

FIG. 8 shows the arrangement after the mold sections 74',76' have beenbrought together and pressed against the subassembly and the applicationof suitable force, for example about 2,000 pounds. The recesses 80' and84' in the upper and lower mold sections 74' and 76', respectively,define the ribs or corrugations 70' in both opposite faces of the anodeassembly as previously described. At the same time, protuberance 78 andrecess 82 co-operate to shape or form the adjacent inner surfaces oflithium plates 22',24' to have co-operating formations which expose newsurfaces of the lithium plates to each other to form or enhance the bondtherebetween. These co-operating formations defined by protuberance 78and recess 82 are located near the peripheral edges of the lithiumplates 22',24'. In effect, the foregoing provides a flowing or movingborder around the anode assembly, exposing new lithium surfaces to eachother to crimp or seal the lithium plates 22',24' together for bettercohesion. The resulting anode assembly is removed from the mold in amanner similar to the foregoing method.

FIGS. 9 and 10 illustrate a mold for forming the anode assemblyaccording to the present invention. The mold comprises two complimentarysections or plugs, of opposite hand configuration, one of which isdesignated 100, which during use are confined in a suitable nestapparatus for pressing the lithium plates therebetween to shape and formthe anode assembly. The mold plugs and portions of the nest apparatusare of a material and have a structure whereby the need for partingsheets is eliminated. In accordance with the present invention, the moldplugs and portions of the nest are of polyolefin material, for examplehigh density polyethylene or the equivalent, which provides easyseparation of the mold and nest sections from the lithium plates afterpressing. By way of example, such material can be Resinol type "F", ahigh density polyethylene commercially available from Allied ResinousProducts, Inc. In addition, the face of each mold section or plug isformed with recesses to define the ribs or projections on the anodefaces, and these recesses on the mold sections are shaped to enhance themechanical release of the lithium plates from the mold sections afterpressing.

Referring now to FIG. 9, mold section 100 includes a working face 102which is flat and smooth and has a peripheral shape or configurationcorresponding approximately to that of the anode plates 22,24. Inparticular, mold section 100 has an arcuate edge portion 104corresponding to the edge of the anode assembly which faces the cellcasing bottom 11 and which meets two outward curved edge portions106,108 extending from the opposite ends of portion 104, an inclined orangled edge portion 110 at the left-hand end as viewed in FIG. 9, astraight edge portion 112 extending therefrom and two surfaces 114,116defining a step at the right-hand end in FIG. 9. The shape orconfiguration of the mold sections can vary depending upon the desiredanode shape or configuration, for example the portions 104 could berelatively straight rather than curved.

The working face 102 of mold section 100 is provided with a plurality ofspaced, generally mutually parallel recesses 120 which are shaped todefine the anode ribs or corrugations 70 shown in FIGS. 3 and 4. Asshown in FIG. 10 each recess has a pair of side walls 122,124 which meetan inner or bottom wall 126. The bottom wall 126 is curved or arcuate,and the side walls 122,124 are relatively straight and inclined, ortapered outwardly. According to a preferred mode of the presentinvention, each of the walls 122,124 is disposed so as to define anangle of about 30 degrees to a plane normal to surface 102. Expresseddifferently, the plane of each wall 122,124 extended outwardly beyondsurface 102 defines an included angle of approximately 60 degrees withsurface 102.

An anode subassembly is provided in the same manner as the foregoingmethod and is placed in the nest along with the lithium plates 22,24 andbetween two mold sections or plugs, each section or plug being likesection 100. No parting sheets are employed in the nest or between themold sections and lithium plates. The mold sections are brought togetheragainst the lithium plates and a force of about 2000 lbs. is applied fora time of about seven seconds. Upon conclusions of the pressingoperation, the mold sections are moved away from the pressed anodeassembly. Separation is very good from each mold section, with theassociated lithium surface separating freely and with no sticking orgalling. The mold according to the present invention combines thereleasing effects of the high density polyethylene material with themechanical release provided by the tapered side walls of the recesses.While the afore-mentioned high density polyethylene material ispreferred, an ultra high molecular weight polyolefin material can beemployed, for example that commercially available from the Polymer Corp.under the designation Polypenco.

FIG. 11 illustrates the afore-mentioned nest apparatus which is in theform of a segmented nest or ring type device comprising three metalhalves or sections 125,126,130 and a pair of inserts 127,128. Inparticular, sections 125,126,130 are joined by tongue and groove joints(not shown) extending from the abutting surface of one section into amating recess in the abutting surface of the other section inco-operation with pin type fasteners 129. Inserts 127,128 are of thesame polyolefin, for example high density polyethylene material, as themold sections. The arcuate edge surfaces of the inserts 127,128 have adegree of curvature corresponding to the desired shape of thecorresponding portions of the peripheral edge of the anode assembly.Section 130 has an angularly disposed inner edge surface correspondingto the angularly disposed portion of the anode peripheral surface, andthe bottom of section 126 facing section 125 and 130 shaped toaccomodate the lid of the assembly as previously described.

In use, one mold section is held in a suitable holding device or fixture(not shown), the anode subassembly and lithium plates are placed in thenest apparatus of FIG. 11 as previously described, and this is placedand held in the fixture so that the one mold section contacts onelithium surface in the desired manner. Then the other mold section isplaced and held in the fixture in contact with the other lithium surfaceand pressure is applied thereafter. During the pressure formingoperation, the nest apparatus simultaneously imparts shape to theperiphery of the formed anode assembly. The inserts 127,128 whichcontact the lithium are of the aforementioned polyolefin material whichreadily releases from the lithium after the pressure forming operationwithout the need for any parting sheets.

After the anode assembly is removed from the nest, the exposed surfacesof lithium elements 22 and 24 are provided with coatings 130 and 132,respectively, of an organic electron donor component material, and thenature of the coatings 130,132 and their role in the cell of the presentinvention will be described in further detail presently. The completedanode assembly is positioned in casing 10 as shown in FIGS. 2 and 4,with the anode operative surfaces spaced from the inner surface ofcasing 10.

The cell of the present invention further comprises an iodine cathodeincluding a region of cathode material 136 within casing 10 andoperatively contacting the exposed surfaces of the lithium elements22,24 and operatively contacting the inner surface of casing 10. Casing10, being of electrically conducting material, serves as the cathodecurrent collector. According to a preferred mode of the presentinvention, the cathode material 136 comprises a charge transfer complexof an organic electron donor component material and iodine. The electrondonor can be any organic compound having a double bond or an aminegroup. The electron donor functions to give the iodine sufficientconductivity for proper cell operation. One preferred form of theorganic electron donor component is polyvinyl pyridine polymer and, inparticular, two-vinyl-pyridine polymer.

The cell of the present invention can be fabricated in the followingmanner. Ferrule 52 is welded to lid 17 at 140, and anode conductorportion 30 is secured in ferrule 52 by means of a glass seal (notshown). The assembly of isolator 42, two washers (not shown) andinsulator 32 is combined with the ferrule-lid assembly, and then theapproximate right angle bend in anode conductor portion 26 is made. Theinsulating element 64 is positioned in place, and if an anode currentcollector is to be used it is spot welded to the conductor portion 26.The foregoing assembly is positioned in the anode pressing fixture andlithium plates 22,24 are placed one on each side and the anode assemblycombination is formed by means of one of the pressure forming methodspreviously described. The resulting combination then is placed in casing10 with lead 30 disposed generally parallel to casing walls 12,13 andwith the outer ends of ferrule 52 and lead 30 located outwardly of theopen end of casing 10. At least one spacer element of materialnon-reactive with iodine can be located between the ribs 70 and adjacentthe lower end of the anode assembly for contacting the inner casing wallto hold the anode in spaced relation to the casing. The material can bethe aforementioned Halar material or the equivalent. A spacer 142 isshown, for example, in FIG. 2, but two spacers positioned at oppositeends of the anode could be employed. Lid 17 is welded to the peripheryof casing 10 at 146. Casing 10 and the combination of parts therein isheld upright with the open end facing upwardly by a holding fixture orother suitable means. Then cathode material is introduced to the casing10 through the opening 150 in lid 17. In particular, the cathodematerial, i.e. depolarizer, is prepared by heating the organic material,i.e. 2-vinyl pyridine polymer, mixed with iodine, to a temperaturegreater than the crystallization temperature of iodine, for exampleabout 300° F. The amount of iodine should be greater than about 50percent by weight of the resulting mixture so that enough iodine isavailable in the cathode material to provide sufficient conductivity forproper cell operation. The resulting mixture is a viscous, flowablesubstance which can be introduced to cell casing 10 by flowing itthrough the opening 150. This may be done with the aid of a funnel-likefilling element in a manner described in the afore-mentioned U.S. Pat.No. 4,210,708. Briefly, the heated cathode material is poured orotherwise introduced to the funnel-like filling element through which itflows into the interior of casing 10. The amount of cathode material 136introduced to casing 10 is sufficient to contact the exposed surfaces ofthe lithium elements 22,24. The inner and adjacent surfaces of opening150 contacted by surfaces of the filling element are kept clean and freeof contamination by cathode material. When filling is completed, thefilling element is removed from lid 17 and a closure element 154,preferably also of stainless steel, or the like, is fitted in place inopening 150 and then welded to lid 17 at 156 as shown in FIG. 3. Aneffective weld results from the clean inner surface and edge of opening150. A terminal element including base 160 and pin 162 can be spotwelded to closure 154 either before or after closure 154 is welded tolid 17.

The lithium-iodine cell according to the present invention operates inthe following manner. As soon as the iodine-containing cathode material,for example the cathode material 136 in FIG. 2-4, operatively contacts alithium element, solid lithium-iodide electrolyte begins to form at theinterface. In the present illustration this occurs as the outer oroppositely disposed surfaces of the two lithium elements 22 and 24. Anelectrical potential difference will exist between the anode lead 30 andcathode terminal pin 162 because casing 10 is of electrically conductivematerial and operatively contacts the iodine-containing material toserve as a cathode current collector. The mechanism by which theforegoing is accomplished is believed to include migration of lithiumions through the electrolyte whereby the lithium ion is the ionicspecies in the cell. The exact mechanism by which the iodine-containingcathode material 136 and lithium elements 22 and 24 come into operativecontact through coatings 130 and 132, respectively, is not known. Themechanism could involve migration of iodide ions from material 136through coatings 130,132 to elements 22,24 or migration of lithium ionsfrom elements 22,24 through coatings 130,132 to material 136.

The material of coatings 130,132 on lithium elements 22 and 24,respectively, is an organic electron donor material of the group oforganic compounds known as charge transfer complexes. The material ofthe coatings can be the organic electron donor material used inpreparing the charge transfer complex of the cathode material 136, butother materials can be employed. A preferred material for the coatingsis polyvinyl pyridine, and it is applied to the exposed surfaces oflithium elements 22 and 24 in a manner as described in theabove-referenced U.S. Pat. No. 4,210,708.

The coatings 130 and 132 on lithium elements 22 and 24, respectively,perform several important functions. One is a desirable reduction incell impedance believed to result from a better and improvedelectrically effective contact area between the cathode material andeach lithium element. In particular, when iodine-containing cathodematerial at an elevated temperature comes into contact with an uncoatedlithium surface, there can be some immediate recrystallization of iodineon the lithium surface thereby blocking or preventing operative contactat that point between the lithium element and the complex of organicmaterial and iodine. Coatings 130 and 132 serve as protective coatingsto prevent this problem, functioning as buffers between the pure lithiumplates and the relatively hot cathode material as it contacts theplates. There may be other mechanisms involved in the improvement ofperformance resulting from the use of this coating. As a result, thereis provided a greater utilization of the surface of each anode elementby the cathode material. In addition, the protective coatings 130,132permit a relatively longer handling time during construction of the cellprior to introducing the hot cathode material.

It is important that the iodine-containing material 136 is not allowedto come in contact directly with any portion of the electricalconducting means connected to the lithium members of the anode, inparticular anode conductor portions 26 and 30. Otherwise, this willcause an electronic conduction between the cathode material 136 and theanode conductor sections 26,30 creating an electrical short circuitcondition in the cell. In particular, any migration of theiodine-containing complex of material 136 directly to anode conductorsections 26,30, instead of first reacting with a lithium member of theanode, will result in the condition of electronic conduction therebycreating an electrical short circuit condition in the cell. On the otherhand, when the iodine-containing material 136 contacts only the lithiumportion of the anode this gives rise first to a condition of ionicconduction and results in proper cell operation.

The construction of the cell shown prevents an electrical short circutresulting from migration or flow of iodine-containing material 136. Inparticular, anode conductor portion 26 and the neighboring section ofconductor portion 30 are sealed within the sandwiched or pressure bondedassembly of lithium elements 22,24. This seal is enhanced by the formingof the peripheral border or margin 88 on the faces of the lithiumelements 22,24 during the pressing operation. In particular, formingborder 88 during the pressing operation enhances the lithium-lithiumbond between elements 22,24. The absence of any strap or frame aroundthe major portion of the periphery of the anode assembly and theterminations of ribs 70 in the manner defining border 88 on both facesof lithium elements 22,24 combine to produce an unimpeded anduninterrupted flow of lithium during the anode forming operation. This,in turn, results in greatly increased lithium-to-lithium bonding orcohesion with reduced anode forming pressures as previously discussed inconnection with FIGS. 5 and 6.

The improved seal also can be formed alternately by the border crimpingor similar formation, which exposes new lithium surfaces around theinner peripheral faces of the anode assembly, resulting from thealternative method previously discussed in connection with FIGS. 7 and8.

The foregoing arrangement together with the combination of insulator 32,isolator 42, ferrule 52 and glass seal between ferrule 52 and conductorportion 30 provides an anode structure which is completely sealed withthe exception of the exposed lithium surface portions of the anode whichare available to the cathode material 136. All parts of the anodeconductor portions 26 and 30 extending therefrom are shielded from thecathode material, and from the cell casing. Furthermore, the sealedassembly advantageously is completed before the entire cell isassembled, in particular before cathode material 136 is added thereto.Insulator 32 of Halar or similar material which is non-reactive withiodine surrounds and protects anode lead portion 30 between lid 17 andthe lead portion 26 within lithium elements 22,24. Ferrule 52 surroundsand protects lead portion 30 from a point within lid 17 and adjacentinsulator portion 36 to a point outside casing 10.

By having all parts of anode conductor portions 26,30 shielded or sealedfrom cathode material 136 and from the metal casing 10, no insulation isneeded between the cathode material and the metal casing. The casing canbe completely filled with cathode material which considerably increasesthe iodine contact of the cell as compared to cells requiringinsulation. Another advantage of the cell of the present invention isthat by virtue of the foregoing arrangement, the metal casing becomes avery large cathode current collector thereby improving cell performancedue to the relatively larger amount of cathode material in contact withthe current collector. In addition, providing ribs 70 on the operativesurfaces of the lithium anode elements 22,24 increases the effectivesurface area of the anode elements in operative contact with cathodematerial 136. As previously described, the cathode material not onlycontacts the oppositely directed anode surfaces of increased area butalso contacts a major portion of the peripheral edge and areasimmediately adjacent to the edge thereby further increasing theavailable anode surface area directly in contact with the cathodematerial. Furthermore, the absence of any strap or frame around a majorportion of the anode periphery increases the available volume foradditional cathode material, i.e. depolarizer. The absence of the strapor frame also reduces the chance that voids or incomplete fills willform when the depolarizer material is poured into the casing containingthe anode assembly. This, in turn, increases the actual ampere-hourrating when it is based upon cathode material volume. The foregoingdesirable characteristics are enhanced by the coatings 130,132 oforganic electron donor material. By eliminating the need for an anodeperipheral strap or frame, previously thought to be necessary to sealboth elements of the anode assembly, the cell of the present inventioncan be assembled more quickly and economically and requires fewer parts.In addition, the improved anode molds and forming device or nestaccording to the present invention provides effective separation of theanode from the molds and forming device without the use of partingsheets.

It is therefore apparent that the present invention accomplishes itsintended objects. While several embodiments of the present inventionhave been described in detail, this is for the purpose of illustration,not limitation.

I claim:
 1. An anode assembly for a lithium-halogen cell including ahalogen-containing cathode material, said anode assembly comprising ananode electrical conductor sandwiched between a pair of lithium platesdefining substantially oppositely-directed lithium surfaces terminatingin a peripheral lithium edge disposed between said surfaces andcharacterized by a major portion of the length of said peripheral edgebeing uncovered and exposed, a minor portion of the length of saidperipheral edge being covered by an element of electrical insulatingmaterial, thereby increasing the area of lithium for operative contactwith the cathode material of the cell.
 2. An anode assembly according toclaim 1, wherein the areas of said oppositely-directed lithium surfacesadjacent said major portion of said peripheral edge also are uncoveredand exposed.
 3. An anode assembly according to claim 1, wherein at leastone of said oppositely-directed lithium surfaces is shaped to includeformations which increase the surface area thereof.
 4. An anode assemblyaccording to claim 3, wherein said formations are included on both ofsaid oppositely-directed lithium surfaces.
 5. An anode assemblyaccording to claim 3, wherein said formations are elongated each havingterminations at both ends thereof spaced inwardly a short distance fromsaid peripheral edge thereby defining a material border region betweensaid peripheral edge and said terminations of said formations.
 6. Ananode assembly according to claim 1, wherein said anode electricalconductor is of narrow width and contacts only minor portions of thesurface areas of the inner surfaces of said lithium plates.
 7. An anodeassembly according to claim 1, wherein the inner surfaces of saidlithium plates include co-operating formations which are shaped toexpose new surfaces of the lithium plates to each other to enhance thebond therebetween.
 8. An anode assembly according to claim 7, whereinsaid co-operating formations are located near said peripheral edge. 9.An anode assembly according to claim 1, wherein said peripheral lithiumedge is disposed substantially at right angles to said surfaces.
 10. Ananode assembly according to claim 1, wherein said lithium plates arepressure bonded together and against said conductor.
 11. An anodeassembly for a lithium-halogen cell including a casing of electricallyconductive material and halogen-containing cathode material within saidcasing, said anode assembly comprising an anode electrical conductorhaving a portion sandwiched between a pair of lithium plates definingsubstantially oppositely-directed lithium surfaces terminating in aperipheral edge between said surfaces and characterized by a majorportion of the length of said peripheral edge being uncovered andexposed so as to increase the area of lithium for operative contact withthe cathode material of the cell, said anode electrical conductor havinganother portion adapted to extend within and through said casing, andinsulator means enclosing said other portion of said anode conductor.12. An anode assembly according to claim 11, wherein said lithium platesare pressure bonded together and against said conductor portion.
 13. Ananode assembly according to claim 11, wherein said anode electricalconductor is of narrow width and contacts only minor portions of thesurface areas of the inner surfaces of said lithium plates.
 14. An anodeassembly according to claim 11, wherein the inner surfaces of saidlithium plates include co-operating formations which are shaped toexpose new surfaces of the lithium plates to each other to enhance thebond therebetween.